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From: mcferrin@inuxc.UUCP (P McFerrin)
Newsgroups: net.unix,net.unix-wizards
Subject: Re: Machine check, type 0 (VAX 780)
Message-ID: <1163@inuxc.UUCP>
Date: Fri, 6-Sep-85 03:08:00 EDT
Article-I.D.: inuxc.1163
Posted: Fri Sep  6 03:08:00 1985
Date-Received: Sat, 7-Sep-85 13:19:15 EDT
References: <204@drivax.UUCP> <1162@inuxc.UUCP> <282@decwrl.UUCP>
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Organization: AT&T Consumer Products, Indianapolis
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Xref: watmath net.unix:5591 net.unix-wizards:14745

> > > Does anyone know what 'Machine check, type 0' is on a VAX 780?
> > > ....
> > > ....
> > > 
> > > { ihnp4, amdahl, mot }!drivax!alan
> > 
> > This problem is caused by a device on the Unibus.
> > It occurrs when a device fails to reply with its vector address when requested
> > so during a bus-request/bus-grant protocol.  This can be a tough problem
> > to isolate.  I know of no proceedure to find the culprit except by
> > replacing one board at a time.
> > 
> > Another cause of this problem can be external wiring to a DR-11 interface
> > (parallel i/o).  Noise on the request A or B lines can cause the DR11
> > to withdraw in the middle of a bus-request/bus-grant protocol.
> > 
> > It is a hardware problem.
> 
> Hi there.
> There may have been more information in Alan Fargusson's message
> that I did not see but P McFerrin is wrong in saying that the problem
> is a UNIBUS device.  Don't confuse "read timeout" with UNIBUS timeouts
> (which are handled somewhat differently on VAX-11/780's than PDP-11's).
> A "CP read timeout fault" is caused when the cpu tried to do a data
> reference and the bus control logic could not gain access to the SBI
> or it received no response for so many cycles (or the requested
> location [nexus?] responded with Busy (or something to that affect)
> for so many cycles).  
> 
> In the case of a failed UNIBUS access, the UBA will cause an interrupt
> and in 4.2 (Ultrix-32), an error message will be printed, and the system
> will attempt to reset the UBA.  System V's actions do not seem straight
> forwart to me (but I only looked at it for about 10 min) but it appears
> to print out the contents of some registers and then return.
> 
> This is not to say that there couldn't be a problem with Alan's UBA ...
> 	aps.

We have several VAXens here with most of them configured with a DR11-C
parallel interface connected to Datakit VCS.  If the cable connector from
the DR11-C is not plugged in all the way, it is a guarantee "CP Read time-out"
fault.  Unix them attempts a "warm-restart" but can't and prints "Power Fail
error".  Now the qusetion: is this an Unibus device causing the error??
It is reproducable on several of our systems.